Grinding wheel truing apparatus



Nov. 7, 1950 c. E. SWEETSER 2,523,621

GRINDING WHEEL TRUING APPARATUS Filed July 11, 1947 lv yve-r tor' Chauncey E. Sueetsew Flt-i orney Patented Nov. 7, 1950 GRINDING WHEEL TRUING APPARATUS Chauncey E. Sweetser, Worcester, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Application July 11, 1947, Serial N0. 760,366

4 Claims. (01. 51-1345) The invention relates to apparatus for truing grinding wheels, especially for truing diamond grinding wheels and of these especially for truing diamond grinding wheels bonded with the harder bonds such as with metal bond or vitrified ceramic bond.

One object of the invention is to provide a simple and dependable apparatus which can be used on a wide variety of grinders for truing the grinding wheel thereof. Another object is to provide a truing tool for diamond grinding wheels which will shape them accurately. I Another object is to provide a tocl of the character indicated which is capable of truing the hardest of grinding Wheels. Another object of the invention is to provide a truing tool of the character indicated whose wearable part is relatively inexpensive and easily replaced. Another object of the invention is to provide a rotary truing tool with an effective control to enable it to perform a. truing operation on very hard grinding wheels accurately. Another object of the invention is to provide a truing tool to true grinding wheels, especially diamond grinding wheels, which is resistant to wear.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements and arrangements of parts, all as will be exemplified in the structure to be hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings in which is illustrated one of various possible embodiments of the mechanical features of this invention,

Figure 1 is an end elevation of truing apparatus constructed in accordance with the invention,

Figure 2 is a plan View of the apparatus of Figure 1,

Figure 3 is a view, partly in side elevation and partly in axial section, of the apparatus,

Figure 4 is a cross-sectional view taken on the line 4-4 of Figure 3.

Referring to Figures 1, 2 and 3 the apparatus has a, base II] which is shown as a fiat piece of metal, rectangular in plan, and which has slots II, one on each side, whereby the base II] can be clamped to the table or other part of the grinder, as by means of bolts not shown. The base I is integral with an upstanding housing l2 which has at one end a flange I3. The base I0;-the housing I2 and the flange I3 may be one piece of metal, for example a piece of cast iron.

The housing I2 is bored all the way through to form a series of coaxial bores the axis of which 2 is parallel to the bottom of the base I0; As shown in Figure 3 and working from left to right there is first an integral inwardly extending flange I4, then along bore I5 next internal screw threads l6, then a bore I! of larger diameter than that of the bore I5 and finally a bore IB of larger diameter than the bore II. In'contactwith the flange I4 is the outer race I9 of a ball bearing 20 which race is pressed against the flange I4 by a sleeve 2| which closely fits the bore I5 and which is engaged by a ring nut 22 whose threaded exterior is in engagement with the internal screw threads I6. In the bore I1 is a spring 23 which at the left hand end engages a washer 24 in contact with the ring nut 22 and which spring 23 at the right hand end engages a sleeve 25 inthe bore I8, the right hand end of the sleeve 25 being cut away to receive the outer race26 of a ball bearing 21. The sleeve 25 is slidable in the bore I8 but is prevented from turning therein by means of a pin 28 through the housing I2 which pin 28 engages a slot 29 in the sleeve 25. I

The ball bearing 20 has an inner race 30 which nicely fits a long cylindrical portion 3| of a spindle 32. The left hand side of the race 30 is in engagement with a flange 33 of the spindle 32, while the right hand side ofthe race 30 is engaged by a long sleeve 34 fitting the cylindrical portion 3|. On the cylindrical portion 3| and engaging the right hand end of the long sleeve 34 is the inner race 35 of the ball bearingf21. A nut 36 screwed onto a threaded'portion 3'! of the spindle 32 engages the inner race 35 and by tightening the nut 36 the two races 30 and 35are held tightly on the spindle 32 in fixed spaced relationship. It will now be seen that the fore going provides a precision mounting for rotation of the spindle 32 in the housing I2 since all play is taken out of the ball bearings by the spring 23 which through the sleeve 25 thrusts the race 26 to the right thus thrusting the entire spindle 32 to the right to take out all play in the ball bearing 20 whose outer race I9 is rigidly held as described; Thespindle 32 will thus run true and with little friction, due to the ball bearings, in the housing, I2 and it is noted that the axis of the spindle 32 is parallel to the plane of the bottom of .the base I0 and is perpendicular to the long sides of the precision machine having a slot for affixing T-b0lts or equally well the base It] can be held in positionby a, magnetic chuck and the'spindle' 32 thereby accurately and rigidly located. In

order to lubricate the ball bearings 20 and 2! there may be provided an oiling plug 38 screwed into the housing l2 and extending into the bore IT. The washer 24 slightly clears the sleeve 34 to allow the oil to work to the left while the clearance between the sleeve 25 and the sleeve 34 will allow the grease to work to the right. A felt washer, or the like, 39 is located between the flange l4 and the flange 33 to keep the oil from coming out of the bore in the housing I2.

Adjacent the flange 33 on the spindle 32 is a larger flange 49 which serves to hold the Washer 39 in place and also positions a grinding wheel 4| which has the usual central hole and-which fits on a cylindrical portion 43 of the spindle 32. The left hand end of the spindle 32 has a screw threaded portion 44 on which may be mounted'a nut 45 engaging a washer 46 to clamp the grinding wheel 4| tightly against the flange 40.

Referring now to Figure 4 and the right hand side of 'Figure 3, I provide a centrifugal friction brake which will now be described. As shown in.

Figure 3 the spindle 32 has a tapered portion50 on which fits a cylindrical metal member 5 having a tapered hole 52 to fit the tapered portion 50. The cylindrical member 5! is rigidly held on'the spindle 32 by means of. a nut 53 onthe threaded end portion 54 of the spindle 32, the'nut 53 en--' gaging a washer 55 which is-in engagement with the side of the cylindricalmetal member 5|.

A plurality of. threaded bores 56'are formed in the cylindrical member 5| whichbores are radial to the cylindrical member 5|. These threaded bores 56 extend right into the tapered hole 52. They merge with largerunthreaded bores 51 which in turn merge into rectangular cut-outs 58 extending right across" the periphery of the cylindrical metal member 5|. In the cut-outs 58 are shoes 59 whose. exterior surfaces are cylindrical segments forming a continuation of the cylindrical exterior surface of the member 5|. The shoes 59 have cylindrical-extensionsfifl which fit in the bores 51. Countersunk in the shoes 59 and inthe cylindrical extensions 30 are cylindrical holes 6| which do not. extend clear'through the inner ends of the cylindrical" extensions 65-. However, there are small holes in the inner ends of the-extensions 60 through which pass screws 63 in engagementwith the threads of the bores 56. In the cylindrical holes 6| and surrounding. the screws 63- and extending between the inner ends of the extensions 60' andthe heads of the screws 63 are springs 64.

When. the grinding wheel 4| is rotated; it rotates the spindle 32 which rotates the cylindrical metal member 5|. The shoes 59, which are preferably made of metal, have. a certain mass and preferably they'all have the same mass. Centrifugal force actsradially outward on the shoes- 59 slightly, whereupon the spring tension will automatically increase... I provide a cylindrical internalv brake surface- B5 which. may be the interior of a cap 66 fitting over the cylindrical end 61 of the housing. 2 and. resting against the flange 3 and being secured in place by screws 68. Increase of angular velocity after the shoes 59 have started to move will finally bring them into contact with the surface 65- which. will apply a 4 friction to the apparatus to prevent further increase of angular velocity.

The apparatus in the cap 66 is a speed governor operating on the centrifugal force-friction principle. This particular governor will control the angular velocity of the grinding wheel 4| to within something better than 10% for most practical. operations and this measure of control is satisfactory for truing diamond grinding wheels. Any other type of speed governor which will exercise similar control of the speed of the grinding wheel 4| may be used in place of the particular governor described. Many varieties of speed governors are now known to the art so therefore I need not describe any other type. It is desirable however that the governor employed permit easy starting of the tool and most governors will do so. It will be seen that when the grinding wheel 4| starts to rotate, there is no friction whatsoever produced by the governor until a speed close to the control speed: is reached; This is true of the present governor and will'be true of other governors where centrifugal force moves an element which finally becomes a friction ele ment. I prefer such type ofgovernors.

The apparatus of the present invention can be used on practically any kind of grinder, such'as surface grinders, tool and cutter grinders, chip; breaker grinders, carbide toolgrinders, cylindrical grinders, centerless grinders, internal grind ers and stone cutting machinery. It issufli'cient to secure the base IE to the'appropriate part of the machine and then, using'the' precision feed; usually a cross. feed; of the machine, feed the grinding wheel of the machine into the grinding wheel 4! of this apparatus. As aforesaid it is convenient to use a magnetic chuck, if suchis' available, to hold the base l0 in position. Otherwise bolts or clamps can be used. For different kinds and sizes of machines the base lll'ma-y assume many different shapes in order to fit particular machines properly.

A wheel 4! having been selected which is itself true, and the base l0 having been secured in place on the grinder, at the desired angle, the diamond grinding wheel of any varietysuchv as vitrified or metal or resinoid bonded is slowly fed into contact with the wheel 4|. The wheel4| due to the anti-friction bearings rapidly picksup speed until the governed speed is reached. Speeds of grinding wheels are usually stated in terms of peripheral velocity rather than angular velocity, because it is the peripheral or surface velocity which determines the cutting rate. Most diamond grinding wheels are driven at angular velocities whichwill produce surface speeds at between 4500 and 6500 surface feet per minute; A standard speed for a diamond grindingQwheeL is 5500 surface feet per minute, either peripheral velocity or the surface velocity of an annular face which does. the grinding in the case of cup wheels. I have found that they truingwheel 4|- should revolve at between 1000 and. 2000 surface feet per minute for good results. I now prefer about 1500 surfacefeet. per minute for the wheel 4| when the diamond wheel is moving at:5500 surface feet per minute- The governor. inv the cap 66 can readily be adjusted togive this velocity. 1

Thegrinding wheel 4| for'best results shouldbe a wheel made of silicon carbide abrasive bonded. with vitrified bond. However it is to be understood that other abrasives .could be used to make the wheel 4 l Ibelieve however that silicon car- 5. bide will give the best results on all kinds of diamond grinding wheels.

The grit size of the abrasive of the wheel 4| is determined by the grit size of the diamond abrasive in the wheel to be trued for the best results. For all diamond wheels having diamonds coarser than 6'0' grit size I prefer to use 30 grit size silicon carbide. For diamond grinding wheels having diamonds of grit size 60 to 80 I prefer to use 46 grit size siliconcarbide. For diamond grinding wheels havingdiamonds of 100 to 180 grit size I prefer to use 60 grit size silicon carbide. For metal bonded and vitrified bonded diamond grinding wheels having diamonds of 220 grit size and finer, I prefer to use 80 grit size silicon carbide. "The apparatus of the invention is useful for truing all types of metal bonded and vitrified bonded diamond grinding wheels of which I have knowledge and it is useful for truing resinoid bonded diamond grinding wheels up to 220 grit size.

With regard to the grade and structure of the grinding wheel 4|, I prefer medium structure and in most cases the grade hardness should be medium but this is dependent upon the extent of contact between the diamond wheel and the wheel 4| and upon the grit size of the diamond wheel. If the contact is narrow, that is below a quarter of an inch, harder grades of wheels 4| should be used. Also if the grit size of the diamond wheel is on the coarse side, the grade hardness of the wheel 4| should be increased and vice versa.

A few examples will now be given of specifications for the wheel 4| for corresponding specifications of the diamond wheels and it is understood that in all cases the diamond wheel surface is moving at 5500 surface feet per minute and the wheel 4| is governed to cause its peripheral surface to move at close to 1500 surface feet per minute.

For truing a so-called straight diamond wheel, that is to say comprising a cylindrical disc grinding on the periphery, of dimensions 8" in diameter by thick, having 100 grit size diamonds bonded with vitrified bond with 25 volume per cent of diamonds, grade N, a silicon carbide wheel 4| of 60 grit size, grade L and structure 5 is preferred. For truing a cutting-01f wheel consisting of a disc 12" in diameter and of an inch thick comprising 12 volume per cent of 80 grit size diamonds bonded with grade N metal bond, I prefer a wheel 4| having 46 grit size silicon carbide bonded with vitrified bond to grade 0 and structure 5.

In using the apparatus of the present inverftion the grinding wheel 4| is traversed across the face of the grinding wheel to be trued. The relative motion between the grinding wheel 4| and the diamond wheel is thus like the relative motion between a truing diamond and an ordinary grinding wheel. Since there are so many different kinds of grinders the foregoing will be made clear by reference to a surface grinder having a flat table and a grinding wheel spindle above the table parallel to it. If it is desired to true a straight cylindrical diamond wheel which grinds on the periphery on such a machine, the diamond wheel is secured to the spindle of the machine and the apparatus of this invention is secured to the table of the surface grinder with its spindle 32 parallel to and underneath the spindle which holds the diamond wheel. The down feed of the surface grinder is used to cause the wheels to approach. This is the infeed for wheel 4| and the diamond wheel to be trued.

The down feed is adjusted so that the two wheels will just make contact and then the cross feed is used'to traverse. After one or two passes the down feed may be used to cause a further infeed between thewh'eels. In using this apparatus an infeed of one thousandth of an inch is a good infeed. Lesser infeeds can be used but in most cases the infeed between successive passes should not be much greater than a thousandth of an inch.

. It is important for the life of the apparatus that grit be kept away from the ball bearings 20 and 21. The washer 39 servesto some extent to keep the abrasive dust from getting inside of the housing I2. Other means of sealing the housing |'2 can be provided. Most of the operations performed so far have been done dry partly because of danger of getting lubricant loaded with 'abra-' sive into the bearings. Good results have been obtained in dry operations. However in certain cases it may be desired to use a grinding lubricant such as a soluble oil water mixture in performing the truing operation.

For the governor, good results have been had using shoes 59 made of bronze and a brake surface 65 of steel. The friction combination was therefore bronze against steel. This combination is resistant to Wear and while it also makes a good bearing, thecombination of large diameter and pressure causes sufficient friction to be developed to govern the speed satisfactorily. However other materials can be used for the friction elements.

It will thus be seen that there has been provided by this invention an apparatus in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. Truing apparatus for grinding wheels comprising a spindle having a portion upon which a truing grinding wheel can be mounted, a truing grinding wheel secured on said portion, said truing grinding wheel comprising crystalline abrasive in a vitrified bond, a housing, hearings in said housing journalling said spindle, a member connected to and on said spindle and mounted for rotation, brake shoes mounted on said member, springs operating against said brake shoes, and a brake drum surrounding said brake shoes 60 whereby when said truing grinding wheel is rotated by a grinding wheel to be trued the truing grinding Wheel will rotate at a predetermined rate.

2. Truing apparatus for grinding wheels comprising a spindle having a portion upon which a truing grinding wheel can be mounted, a truing grinding wheel secured on said portion, said truing grinding wheel comprising crystalline abrasive in a vitrified bond, a housing, bearings in said housing journalling said spindle, a member connected to and on said spindle and mounted for rotation, brake shoes mounted on said member, springs operating against said brake shoes, screws bearing against said springs to adjust the pressure of said springs against said brake; shoes, and a; brake drum surroundin said brake shoesv whereby: when said truinggrinding wheeltisrotated bya grinding wheel to be trued the truing grinding wheel will rotate. at a predetermined rate. a 1

3-. In truing apparatus as claimed in claim 1, the combination with the parts and: features therein specified, of the further feature that the truinggrinding; wheel on the spindle is a silicon carbide wheel. 7 I V 4. In truing apparatus as claimed in claim 2, the combination. with the parts and features therein specified, of the further feature thatthe truing' grinding Wheel on the spindle is a silicon carbide wheel.

CI-IAUNCE-Y E. SWEETSERL 5 Number Name 1 Date. 574,209, McFadden' ':Dec; 29; 1896 1,075,227 Sheehan' ':.Oct. 7*, 19:13- 1,395,394 -Conners Nov.,, 1, 1921 10 v1,777,607 Elcholm-et all ,'Oct. '1, 1930 1,811,933 i Hahnhorst etsal; June 30;;1931e 1,$ )67,li7 Nelson 617 al July- 2411934 FOREIGNPATENTS I 5 Nufriber} Country I Date 7 r 25,216 Great Britain Nov 29, 1898;

REFERENCES CIT-ED v 1 I The following references are of recordin'the file of this'patent: I 'l-"f' 1 s UNITE]; sr TEs, PATENTS, j 

